The present invention relates to downhole tools and methods for measuring formation properties and/or inspecting or manipulating the inner wall or casing of a wellbore. In particular, it relates to such tools and methods for use in horizontal or high-angle wells.
With the emergence of an increasing number of non-vertically drilled wells for the exploration and recovery of hydrocarbon reservoirs, the industry today experiences a demand for logging tools suitable for deployment in such wells.
The conventional wireline technology is well established throughout the industry. The basic elements of down hole or logging tools are described in numerous documents. In the U.S. Pat No. 4,860,581, for example, there is described a down hole tool of modular construction which can be lowered into the wellbore by a wire line. The various modules of the tool provide means for measuring formation properties such as electrical resistivity, density, porosity, permeability, sonic velocities, density, gamma ray absorption, formation strength and various other characteristic properties. Other modules of the tool provide means for determining the flow characteristics in the well bore. Further modules include electrical and hydraulical power supplies and motors to control and actuate the sensors and probe assemblies. Generally, control signals, measurement data, and electrical power are transferred to and from the logging tool via the wireline. This and other logging tools are well known in the industry.
Though the established wireline technology is highly successful and cost-effective when applied to vertical bore holes, it fails for obvious reasons when applied to horizontal wells.
In a known approach to overcome this problem, the logging tool is mounted to the lowermost part of a drill pipe or coiled tubing string and thus carried to the desired location within the well.
This method however relies on extensive equipment which has to be deployed and erected close to the bore hole in a very time-consuming effort. Therefore the industry is very reluctant in using this method, which established itself mainly due to a lack of alternatives.
In a further attempt to overcome these problems, it has been suggested to combine the logging tool with an apparatus for pulling the wireline cable through inclined or horizontal sections of the wellbore. A short description of these solutions can be found in U.S. Pat. No. 4,676,310, which itself relates to a cableless variant of a logging device.
The cableless device of the U.S. Pat. No. 4,676,310 comprises a sensor unit, a battery, and an electronic controller to store measured data in an internal memory. Its locomotion unit consists of means to create a differential pressure in the fluid across the device using a piston-like movement. However,,its limited autonomy under down hole conditions is perceived as a major disadvantage of this device. Further restricting is the fact that the propulsion method employed requires a sealing contact with the surrounding wellbore. Such contact is difficult to achieve, particularly in unconsolidated, open holes.
Though not related to the technical field of the present invention, a variety of autonomous vehicles have been designed for use in oil pipe and sewer inspection. For example, in the European patent application EP-A-177112 and in the Proceeding of the 1993 IEEE/RSJ International Conference on Intelligent Robots and Systems, a robot for the inspection and testing of pipeline interiors is described. The robot is capable of traveling inside pipes with a radius from 520 mm to 800 mm.
In the U.S. Pat. No. 4,860,581, another robot comprising a main body mounted on hydraulically driven skids is described for operation inside pipes and bore holes.
In view of the known logging technology as mentioned above, it is an object of the present invention to provide a down-hole tool and method which is particularly suitable for deviated or horizontal wells.
The object of the invention is achieved by methods and apparatus-as set forth in the appended claims.
An autonomous unit or robot according to the present invention comprises a support structure, a power supply unit, and a locomotion unit. The support structure is used to mount sensor units, units for remedial operations, or the like. The power supply can be pneumatic or hydraulic based. In a preferred embodiment, however, an electric battery unit, most preferably of a rechargeable type, is used.
The autonomous unit further comprises a logic unit which enables the tool to make autonomous decisions based on measured values of two or more parameters. The logic unit is typically one or a, set of programmable microprocessors connected to sensors and actuators through appropriate interface systems. Compared to known devices, such as those described in U.S. Pat. No. 4,676,310, this unit provides a significantly higher degree of autonomy to the down hole tool. The logic unit can be programmed as a neural network or with fuzzy logic so as to enable a quasi-intelligent behavior under down hole conditions.
As another feature, the improved down hole tool comprises a locomotion unit which requires only a limited area of contact with the wall of the wellbore. The unit is designed such that during motion an essentially annular region is left between the outer hull of the autonomous unit and the wall of the wellbore. This allows well fluid to pass between the wall of the wellbore and the outer hull of tool. The essentially annular region might be off-centered during operation when, for example, the unit moves by sliding at the bottom of a horizontal well. Again compared to the device of U.S. Pat. No. 4,676,310, no sealing contact with the surrounding wall is required. Hence, the improved device can be expected to operate, not only a casing, but as well in an open hole environment.
Preferably, the locomotion unit is wheel or caterpillar based. Other embodiment may include several or a plurality of legs or skids. A more preferred variant of the locomotion unit comprises at least one propeller enabling a U-boat style motion. Alternatively, the locomotion unit may employ a combination of drives based on different techniques.
Among useful sensor units are (1) flow measurement sensors, such as mechanical, electrical, or optical flow meters; (2) sonic or acoustic energy sources and receivers; (3) gamma ray sources and receivers; (4) local resistivity probes; and (5) images collecting devicesxe2x80x94e.g., video cameras.
In a preferred embodiment, the robot is equipped with sensing and logging tools to identify the locations of perforations in the well and to perform logging measurements.
In variants of the invention the down hole tool comprises the autonomous unit in combination with a wireline unit which in turn is connected to the surface.
The wireline unit can be mounted on the end of a drill pipe or coiled tubing device. However, in a preferred embodiment, the unit is connected to the surface by a flexible wire line and is lowered into the bore hole by gravity.
Depending on the purpose and design of the autonomous unit, the connection to the wireline unit provides either a solely mechanical connection to lower and lift the tool into or out of the well, or, in a preferred embodiment of the invention, means for communicating energy and/or control and data signals between the wireline unit and the robot. For the latter purpose; the connection has to be preferably repeatedly separable and re-connectable under down hole conditionsxe2x80x94that is, under high temperature and immersed in a fluid/gas flow. In a preferred embodiment, the connection system includes an active component for closing and/or breaking the connection.
These and other features of the invention, preferred embodiments and variants thereof, possible applications thereof, and advantages thereof will become appreciated and understood by those skilled in the art from the detailed description and drawings following below.